1. Field of the Invention
The present invention relates to an ophthalmic apparatus such as an eye refractive power measurement apparatus which measures eye refractive power of an examinee's eye.
2. Description of Related Art
Conventionally, in order to obtain an estimate of a corrective diopter when prescribing a corrective such as spectacles, there is used an eye refractive power measurement apparatus which projects light of a measurement target onto a fundus of an examinee's eye, detects the light reflected from the fundus by a photodetector, and measures eye refractive power of the eye based on a result of the detection (see Japanese Patent Application Unexamined Publication No. 2007-89715 (corresponding to U.S. Pat. No. 7,452,078)). In addition, there is known an eye refractive power measurement apparatus in which a target presenting optical system includes an optical system for correcting a spherical refractive error and an astigmatic refractive error of an examinee's eye (see Japanese Patent Application Unexamined Publication No. 2006-280613 (corresponding to U.S. Pat. No. 7,281,798)).
Visual acuity of an eye can vary depending on an ambient brightness. This is because a pupil size of the eye varies depending on the ambient brightness, so that its optical aperture effect varies a depth of field, or that aspherical properties of a cornea and a crystalline lens cause different influences of aberrations. At dusk or night (scotopic vision), the pupil size is increased, and accordingly visual acuity varies, so that enough visual acuity cannot be obtained by using a corrective such as spectacles which has been prescribed in consideration of a daytime brightness (photopic vision).
In order to check a difference between visual acuity in the scotopic vision and visual acuity in the photopic vision, a visual acuity test is performed while actually changing the ambient brightness by using a target presenting apparatus separate from the eye refractive power measurement apparatus. However, it is necessary to wait for adaptation of the pupil size to the ambient brightness, and therefore, the test takes a long time and an immediate comparison of visibilities in the scotopic vision and in the photopic vision cannot be performed. In addition, when the ambient brightness is changed from the scotopic vision to the photopic vision, the examinee perceives glare.